Math Co-procs

[Sean Eric Fagan]

In article <276f6aae-1decomp.unix.sysv386 at tronsbox.xei.com> tron1 at tronsbox.xei.com (HIM) writes:
>Now, the question.... many of the replies I got told me that the SysV math
>code for using the math co-proc is really for the 80287 for compatibility
>reasons. So this means that these are my questions...

Actually, if I remember correctly, they are both '287 and '387.  The code
determines what kind of fpu is available, and chooses which code to use.
(Note:  this is how SCO does things; I may be confusing the SCO devsys with
the stock 3.2 devsys.  Sorry if I'm wrong...)

>1) Will it matter if the OS really did think it was a 80387 ? If it is
>   really only gonna generate 80287 code then....

I suspect the problem is that the *386* gets confused.  If it expects
certain signals to come from the FPU, and the FPU doesn't have the
capability of generating said signals, then the chip will just... wait.

>2) My BIOS only has a 80287 on/off register, does ISC check the chips or the
>   to determin the FPU type ? (If the bios, then again, we will be ok).

No, I think it queries the FPU itself.  If there isn't one, then the
operation will fail, and the OS knows to use the emulator.  If it doesn't
fail, it can get the FPU type from the FPU.

>3) Could a program with root priviledge go into the kernal and FORCE SET
>   the 80287 flag if the 8037 flag gets set wrongly ?

Ugh... you *could*, by writing to /dev/kmem, but I don't know if you want
to.  If the machine actually boots and gets to the OS, I suspect you won't
run into any problems.  But you'd have to try it, I guess...

-- 
Sean Eric Fagan  | "I made the universe, but please don't blame me for it;
sef at kithrup.COM  |  I had a bellyache at the time."
-----------------+           -- The Turtle (Stephen King, _It_)
Any opinions expressed are my own, and generally unpopular with others.